1. Technical Field
The present invention relates to a projection optical system and a projection type image display device equipped with the projection optical system adapted to project an image, which is formed by a liquid crystal panel or the like, on a screen.
2. Related Art
As a projection optical system having a wide angle of view of which a half angle of view is approximately 60 degrees, capable of obtaining a large screen by performing projection at close range, there exists a projection optical system having a refracting optical section composed of a plurality of lenses (see JP-A-2007-147970). However, in the case in which it is attempted to obtain vary wide angle of view only by the function of the refracting optical section, there arises a fault that the lens particularly located on the magnifying side becomes greatly enlarged. Further, in the case in which it is attempted to achieve wide angle of view only by the function of the refracting optical section, a very large number of lenses become necessary for correcting the chromatic aberration of magnification caused by the negative meniscus lens with strong power particularly located on the magnifying side.
As a method of eliminating the fault in the projection optical system having only such a refracting optical section, there is proposed a projection optical system formed of a refracting/reflecting complex optical system using a refracting optical section, which is composed of a plurality of lenses, and a curved reflecting mirror (see JP-A-2006-235516 (Document 2) and JP-A-2007-079524 (Document 3)). Since a reflecting mirror is used as a measure for obtaining a terminal wide angle of view in these refracting/reflecting complex optical systems, there is a feature that the chromatic aberration of magnification described above is hard to occur compared to the projection optical system provided only with the refracting optical section described above.
However, in the projection optical system disclosed in the Document 2, although the very wide angle of view is assured using the refracting optical section and the concave mirror, the curved mirror is very large compared to the size of the lens of the refracting optical section, and the length of the projection optical system is also very large.
Further, in the projection optical system disclosed in the Document 3, in the example of setting the angle of view to be, for example, approximately 60 degrees, although the mirror size is reduced by combining a concave mirror and a convex mirror, the total length of the projection optical system is very large similarly to in the case of the Document 2. Further, the projection optical system is so dark as to have an F number of 3, which is insufficient for an optical system using a transmissive liquid crystal device. Further, since the two mirrors are aspherical, there is significant difficulty in accuracy and assembling.
In view of the above, in the complex optical system of the related art described above, although the wide angle of view can be obtained, there is a fault that it is difficult to shorten the total length, and at the same time, the size of the mirror becomes problematically large. Therefore, although such a complex optical system does not cause a large problem in the case of a model in which a folded structure can be taken such as a rear projector, the growth in size cannot be avoided in the case of a model to which portability is thought to be important such as a front projector.